The preparation of pH-sensitive Pd catalyst ink for selective electroless deposition of copper on a flexible PET substrate

Abstract

We report on the preparation of a pH-sensitive styrene (St)-co-N, N-dimethyl-dimethylaminoethyl methacrylate (DMAEMA)/Pd ink for fabrication of copper pattern on a flexible PET substrate. The St-co-DMAEMA oligomers are synthesized via free radical polymerization using potassium persulfate as the initiator. The synthesized St-co-DMAEMA copolymer is utilized to self-reduce Pd nanoparticles. The pH-sensitive DMAEMA segments function as stabilizing agent for noble metal nanoparticles in acidic ink solution. On the other hand, ink-jet printing St-co-DMAEMA oligomers become hydrophobic during the electroless plating of copper with a basic bath. Therefore, a copper film with dramatically enhanced adhesion is formed on the PET surface without special pretreatment step before electroless deposition of copper film. This process yields Cu conductor formed by plating for 15 min on PET substrate with resistance 2.5 times that of bulk copper. The cyclic bending test results show that electrical resistance increases only slightly after 1000 cycles and is remained low enough for use in practical applications.